Those working in a hot environment are subject to discomfort, heat exhaustion or heat stroke. Discomfort due to heat greatly reduces worker productivity. Heat exhaustion precludes a continuation of work, and requires immediate medical attention. Heat stroke is often lethal. Workers that wear protective garments in a hot environment are particularly vulnerable to discomfort, heat exhaustion, and heat stroke.
Soldiers are required to where a chemical protection suite if a threat of chemical or biological attack is present. In a hot environment, such as the desert during summer, wearing a chemical protection suit is very uncomfortable, and can quickly lead to heat exhaustion. Firefighters, wearing fire protection suits are also subject to discomfort and heat exhaustion. Many foundry and construction workers also are required to wear protective suites and work in hot environments.
Induction of systemic hypothermia (e.g., a hypothermic state) in a patient may minimize ischemic injury when the patient suffers from a stroke, cardiac arrest, heart attack, trauma, surgery, or other injury or insult to the body resulting in ischemia. For example, in the case where the patient suffers a heart attack, the effectiveness of hypothermia is a function of the depth (e.g., within a temperature range between approximately 30° C. and 35° C. for example) and duration of the hypothermic state as applied to the heart. The effectiveness of the hypothermia is also a function of the amount of time that elapses between the original insult (e.g., heart attack) and achievement of protective levels of hypothermia. Also, for trauma and stroke patients, hypothermia aids in controlling swelling of the patient's brain. Furthermore, surgeons typically use hypothermia during brain and other invasive surgeries to protect the brain from surgical interruptions in blood flow.
It has long been known that hypothermia (body temperature lower than normal) is neuroprotective. Hypothermia has a positive affect on all known mechanisms that lead to secondary brain injury. Hypothermia is routinely used during brain and other invasive surgeries to protect the brain from surgical interruptions in blood flow. Hypothermia has also been shown to be effective in controlling swelling of the brain in trauma and stroke patients.
Systemic hypothermia has historically been applied, such as by immersion of the patient's body in a cool bath, where the depth and duration of hypothermia is limited by the patient's ability to tolerate the therapy. Currently, there are several conventional systemic hypothermia systems available. Such conventional systems include blankets or pads where cooled water is circulated through channels in the walls of the blanket or pad and the patient's body contacts the walls of the blanket.
Attempts have been also made to induce hypothermia in a patient by local cooling the surface of the patient's head. For example, Huyghens et al. (Resuscitation 51 (2001) 275-281) demonstrated that it is feasible to remove a sufficient amount of heat through the scalp to induce hypothermia in an adult using a simple cooling cap.
In another example, a conventional head-cooling device involves a head cap with a gel substance contained within the walls of the cap. Prior to use, for example, a user (e.g., medical technician) places the head-cooling device in a freezer to reduce the temperature of the gel within the cap. During operation, the user fits the reduced-temperature cap to the head of a patient. The gel within the walls of the cap absorbs heat from the head, thereby cooling the head of the patient.
Other conventional devices induce systemic hypothermia in a patient by providing contact between a tissue region of interest and a cooling fluid. For example, one conventional device includes a flexible hood having multiple ribs or studs disposed on the inner surface of the hood. When a user places the hood on a head of a patient, the ribs or studs contact the head and maintain a fluid circulation space between the head and the hood and an edge, defined by the hood, contacts the patient's skin. A negative pressure source draws a cooling fluid through the flexible hood, under negative pressure, to cause the fluid to contact the scalp of the patient and draw heat away from (e.g., cool) the scalp. Furthermore, application of the negative pressure seals the edges of the hood against the skin of the patient (e.g., a region substantially free of hair).
Additionally, intravascular catheter based systems directly cool the blood of the patient with an indwelling heat exchanger mounted on the end of a catheter that resides in the central venous system during use.